1. Field of the Invention
The present invention relates to an additive dispensing cartridge for an oil filter assembly, and to an oil filter incorporating the cartridge. More particularly, the present invention relates to an additive dispensing cartridge containing a beneficial additive composition, and to an oil filter having a centrally located additive dispenser incorporated therein. Even more particularly, the present invention relates to an oil filter in which a centrally located additive dispenser, containing one or more oil-conditioning compounds therein, is operable to slowly release the oil conditioning compounds, over time, into filtered engine oil on the downstream, or ‘clean’ side of the mechanical filter element.
2. Description of the Background Art
Many different types of fluid filters are known. Most such filters use a mechanical or ‘screening’ type of filtration, with a replaceable cartridge having a porous filter element therein, through which the oil is repeatedly cycled to remove impurities.
In the oil filtration art, it is well known that normal operation of an internal combustion engine, particularly a diesel engine, results in the formation of contaminants. These contaminants include, among others, soot, which is formed from incomplete combustion of the fossil fuel, and acids that result from combustion. These contaminants are typically introduced into the lubricating oil during engine operation, and tend to increase oil viscosity and generate unwanted engine deposits, leading to increased engine wear.
The conventional solution to these problems has been to place various additives into lubricating oils, during their initial formulation. In order to combat soot-related problems, many conventional lubricating oils include dispersants that resist agglomeration of soot therein. These work well for a short period, but may become depleted. Additionally, due to the solubility and chemical stability limits of these dispersants in the oil, the service lives of the lubricating oil and the oil filter are less than optimal.
In order to counteract the effects of acidic combustion products, many conventional motor oils include neutralizing additives known as over-based detergents. These are a source of TBN (total base number), which is a measure of the quantity of the over-based detergent in the oil. The depletion of the TBN is an important limiting factor for many internal combustion engines, and in particular for heavy-duty applications with diesel engines.
In order to improve engine protection and to combat other problems, conventional lubricating oils often include one or more further additives, which may be corrosion inhibitors, antioxidants, friction modifiers, pour point depressants, detergents, viscosity index improvers, anti-wear agents, and/or extreme pressure additives. The inclusion of these further additives may be beneficial; however, with conventional methods, the amount and concentration of these additives are limited by the ability of lubricating oils to suspend these additives, as well as by the chemical stability of these additives in the oil. Examples of oil filters which include extra additives for the oil include U.S. Pat. Nos. 4,075,097, 4,144,169, 5,591,330, 5,725,031, and 6,045,692.
An oil filter including a central receptacle for holding and dispensing a solid lubricant in powdered form is disclosed in U.S. Pat. No. 5,032,259 to He et al.
Other solutions have been proposed in addition to the conventional method of mixing additives with lubricating oil. For example, in order to combat the buildup of sludge in oil, U.S. Pat. No. 5,042,617, issued in 1991 to Brownawell, and entitled Method of Reducing the Presence of Sludge in Lubricating Oils; and U.S. Pat. No. 5,478,463, issued in 1995 to Brownawell et al, and entitled Method of Reducing Sludge and Varnish Precursors in Lubricating Oil, each disclose an oil filter and method for reducing the amount of sludge in lubricating oil as it circulates through an engine. These Brownawell patents provide for the inclusion of particles in an oil filter that are oil insoluble and oil wettable, and which complex with sludge, such that at least some of the sludge that these particles come into contact with is immobilized on the particles. The Brownawell '617 patent discloses the inclusion of oil insoluble and oil wettable particles in an oil filter that are retained on a divided substrate, whereas the Brownawell '463 patent discloses the inclusion of such particles that are not retained on a substrate, but are nonetheless retained in the oil filter.
Another Brownawell patent, which relates to the reduction of combustion acids in lubricating oil, is U.S. Pat. No. 5,069,799 issued in 1991 and entitled Method For Rejuvenating Lubricating Oils. This patent discloses an oil filter and method for reducing the amount of combustion acids in lubricating oil. In particular, it discloses a method of rejuvenating lubricating oil, which includes reduction of combustion acids, by serially passing the oil through first a chemically active filter media, then a physically active filter media, and finally an inactive filter media. In this '799 patent, the chemically active filter media includes a strong base, to displace weak bases that have combined with combustion acids. The combustion acid and the strong base then combine to form a salt, which is then physically trapped by subsequent mechanical filter media.
U.S. Pat. No. 5,225,081 to Brownawell discloses method of removing polynuclear aromatics from used lubricating oil. The method of the Brownawell '081 reference involves passing oil through a staged oil filter system, which may include a chemically active filter media. The chemically active filter media is made of a composite material including particles of an active component and a thermoplastic binder, which are a product of a heated extrusion process. Basic conditioners are given as one example of materials suitable for use as chemically active filter media. Activated carbon is also emphasized as a preferred component of the filter media in this reference.
Some designs for multiple stage oil filters are known, such as those disclosed in U.S. Pat. Nos. 4,557,829 and 4,886,599. U.S. Pat. No. 4,886,599 to Bachmann et al. discloses a filter cartridge with sequential concentric cylindrical filter elements, for both chemical and mechanical filtration of oil contained in an oil-sealed vacuum pump.
Other designs for oil filters that contain extra additives and dispense those additives into oil, over time, are disclosed in U.S. Pat. Nos. 5,552,040, and 5,591,330. Some designs are also known for heavy duty coolant filters which release additives over time, such as those disclosed in U.S. Pat. Nos. RE 37,369, 5,741,433, and 5,948,248.
U.S. Pat. No. 6,238,554 to Martin, Jr. et al discloses a fuel filter including an inner housing assembly containing a soluble fuel additive composition.
While the known filters are usable for their intended purposes, the release of supplemental additives from the known filters often takes place either immediately after installation or more rapidly than is needed for protecting the oil. Subsequently, after some time has elapsed, there may be little or no additive left in the filter.
Another problem with many of the known filter designs is that beneficial additives are added to the oil before the oil is mechanically filtered through a filter element. As a result, when the oil is mechanically filtered, some of the beneficial additives that have just been added may be immediately filtered out.
A need still exists in the art for an improved oil filter having a beneficial oil additive incorporated therein, which additive is slowly released over the useful life of the filter. A need also exists for an improved oil filter which could extend the useful life of engine oil, so as to allow a user to extend the time interval between oil changes in a vehicle, particularly a vehicle having a diesel engine.